2.1.2. Film Water Vapour Permeability (WVP)

A film's WVP coefficient is a constant value for water vapour permeability at a specific temperature. A film's permeability is influenced by its chemical composition, morphology, type of permanence, and ambient temperature. WVP is a metric that measures how much moisture may pass through a film. It is more crucial in food preservation to protect a substance from moisture. The results of an investigation into the water vapour permeability of CH-gel films containing various EPPE concentrations are shown in Table 1. The results revealed that raising the EPPE concentration in the CH-gel matrix lowered the film's WVP. Significant changes (*p* < 0.05) were seen between all prepared films. The control film (Ch-0% EPPE) had the maximum WVP (2.34 <sup>±</sup> 0.14 <sup>×</sup> <sup>10</sup>−<sup>10</sup> <sup>g</sup> −1 s <sup>−</sup><sup>1</sup> pa−**<sup>1</sup>** ), followed by Ch-1% EPPE (1.58 <sup>±</sup> 0.09 <sup>×</sup> <sup>10</sup>−<sup>10</sup> <sup>g</sup> −1 s <sup>−</sup><sup>1</sup> pa−**<sup>1</sup>** ), Ch-3% EPPE (1.32 <sup>±</sup> 0.07 <sup>×</sup> <sup>10</sup>−<sup>10</sup> <sup>g</sup> −1 s <sup>−</sup><sup>1</sup> pa−**<sup>1</sup>** ), and Ch-5% EPPE (1.08 <sup>±</sup> 0.06 <sup>×</sup> <sup>10</sup>−<sup>10</sup> <sup>g</sup> −1 s <sup>−</sup><sup>1</sup> pa−**<sup>1</sup>** ). The lower WVP might be attributed to the restricted interaction between water molecules in the film as a result of the crosslinking action of chitosan, glycerol, and EPPE, culminating in less available free water [29]. The low WVP value for food packaging sheets is extremely desirable to reduce moisture transfer between the food and its immediate environment. The films' thickness is an important factor in defining their water barrier characteristics. WVP values are lower in thicker films, as water molecules take longer to flow through the film. Kurek et al. [30] observed comparable behaviour after incorporating blueberry and blackberry extracts into chitosan-based gel films.
